UltraJSON: Malformed/Truncated UTF-8 Accepted and Silently Rewritten in ujson.dumps()_CVE-2026-54911

{
    "lastseen": "",
    "description": "UltraJSON is a fast JSON encoder and decoder written in pure C with bindings for Python 3.7+. Prior to 5.13.0, ujson.dumps() (or ujson.dump() or ujson.encode()) have a reject_bytes=False option. When set, they may accept malformed or truncated UTF-8 byte sequences, silently rewriting them into different Unicode characters instead of rejecting them. This leads to input validation bypass and data integrity issues. This vulnerability is fixed in 5.13.0.",
    "published": "2026-06-22T20:53:07.019Z",
    "modified": "2026-06-22T20:53:07.019Z",
    "type": "cve",
    "title": "UltraJSON: Malformed/Truncated UTF-8 Accepted and Silently Rewritten in ujson.dumps()",
    "source": "GitHub_M",
    "references": "https://github.com/ultrajson/ultrajson/security/advisories/GHSA-3j69-69wj-xqx2\nhttps://github.com/ultrajson/ultrajson/commit/169eaf36b1116fece5034ee79a7a0ef3f6deedcf\nhttps://github.com/ultrajson/ultrajson/releases/tag/5.13.0",
    "id": "CVE-2026-54911",
    "bulletinFamily": "",
    "cwe": [
        "CWE-20"
    ],
    "cvelist": null,
    "sourceData": "ultrajson ultrajson < 5.13.0",
    "sourceHref": "",
    "cvss": {
        "score": 6.5,
        "severity": "MEDIUM",
        "vector": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N",
        "version": "3.1"
    },
    "cvss2": [],
    "cvss3": {
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        "baseScore": 0,
        "baseSeverity": "",
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        "attackComplexity": "",
        "privilegesRequired": "",
        "userInteraction": "",
        "scope": "",
        "confidentialityImpact": "",
        "integrityImpact": "",
        "availabilityImpact": "",
        "cvssV3": {
            "version": "",
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        }
    },
    "href": "",
    "category_name": "CVE",
    "post_link": "",
    "product": "ultrajson",
    "version": "< 5.13.0",
    "vendor": "ultrajson",
    "ai_description": "",
    "ai_severity": "",
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    "ai_score": 0
}